Retaining and securing devices for high temperature applications



July 6, 1965 w. G. MATHESON ETAL RETAINING AND SECURING DEVICES FOR HIGH TEMPERATURE APPLICATIONS Filed June 1, 1962 FIG.2

FIG.3

WILFRID G. MATHESON THEODORE J. PRICENSKI INVENTORS BYCQw ATTORNEY to 3000 and above.

emanating heat back into the hot Zone.

United States Patent s 193 064 RETAINING AND enchants DEVICE non HIGH TEMPERATURE ArrLrcArroNs Wilfrid G. Matheson, Marblehead, and Theodore J. Priceuski, Ipswich, Mass, assignors to Sylvania Electric Products line, a corporation of Delaware Filed June 1, 1962, Ser. No. 199,496 6 Claims. (Cl. 189-36) high temperatures without appreciable deformation or distortion is well known to the art. The applications in which such metals are frequently used are the so-called high temperature vacuum furnaces which can attain temperatures in excess of 1500 C. and often as high as 2500 These furnaces, which are heated by electric power, attain such temperatures in a so-called hot zone which can be disposed inside a pair of concentric heating element sleeves. Because it is necessary to eliminate oxidation insofar as possible, it is essential that the heating operation takes place in an atmosphere free of oxygen and preferably in a vacuum. Usually positioned upon the walls of the furnace and surrounding the heating elements are a series of spaced-apart refractory metal heat shields which reflect and radiate outwardly The positioning of these shields frequently is quite critical so that furnace 'wall destruction is prevented and in order to keep heat loss at a minimum. If the heat shields shift during operation of the furnace due to a deformation of the fastening devices which hold them in place, rigid temperature control tends to be quite diflicult to attain.

In the prior art, the heat shields were usually supported through the surface of tungsten heat shields. When using prior art devices, precise positioning and permanence of installation required drilling tiny holes in these tungsten rods and threading fine wires therethrough. When threaded, the ends of the wires were crimped and abutted against the heat shield. Now the cost of drilling holes in tungsten rods was quite high because of the small diameter of the rod and its density. Product damage fre quency occurred during drilling and even after alignment of the heat shields upon a perfectly drilled rod, shifting during heating was quite common.

We have now discovered that the heat shields can be rigidly disposed at all temperatures in each of the furnace operates in a fixed spacial relation upon our novel re fractory metal hardware. Our refractory metal hardware broadly comprises at least two helically wound refractory metal coils having a pitch of 100 percent or slightly more. One of the helical Winding forms what can be called a bolt, while the other forms what can be called a nut. The thread on the bolt is formed by the external surfaces of the substantially circular convolutions of the Winding and is adapted to enter the bore of the nut and mate with the thread formed by the internal surfaces of the substantially circular convolutions of the latters winding. The diameter of the threads of the bolt are preferably just slightly less than the internal diameter of the nut, thereby allowing easy screw-type insertion and removal. Both the nut and the bolt should be substantially irresilient windings, have convolutions of substantially Bdhdfifid Patented July 6, 1965 circular cross-sectional shape and except as noted later, have a substantially uniform internal and external diameter throughout the length.

Of course, the art has previously used helical windings for joining elements together and afiixing such elements in certain postions. However, such helical windings have previously been fabricated from resilient metals such as spring steel and they have generally been used as locking-type retainers. To the best of our knowledge, no fastening device has previously been fabricated of refractory metals formed into at least a pair of irresilient, mating helical coils. Exemplary of the prior art using helical windings for retaining devices is the United States patent of Herman No. 2,138,919. Therein it is disclosed that two portions of an electrical socket can be held together by a conventional cast bolt which screws into a resilient coil spring nut, the latter abutting against one side of a plug socket. As another example, the United States patent to Staempui, No. 2,022,946 discloses a helical spring coil used for a permanent locking retainer. The coil is positioned within a cylindrical-walled outer jacket and is free to turn therein. When the bolt is fully inserted into the outer jacket, the resilient spring will bias against the threads and cause a form of permanent seating. It is quite apparent, that the inventions disclosed in these patents are not adapted for use in high temperature furnaces and neither can be easily manipulated after an application of heat above about 2000 C.

Accordingly, the primary object of our invention is the retention and precise positioning of elements in a high temperature furnace With retaining devices fabricated of refractory metals formed into the shape of mating helical coils.

A feature of this invention is to use a pair of mating, helically wound coils adapted to screw together and serve as a type of nut and bolt.

A further feature of this invention is that each helically wound coil is formed of refractory metal convolutions having substantially circular cross-sections.

An advantage of this invention is that the refractory metal retaining devices can be heated to high temperatures without deformation or distortion and that they may be easily fabricated Without resorting to expensive drilling or thread tapping techniques.

And yet another advantage of our invention is that heat shields disposed within a high temperature vacuum furnace can be spaced precisely from each other at predetermined distances and such distances will not appreciably change during operation or cooling of the furnace.

Many other advantages, features and objects of the present invention will become manifest to those conversant with the art, upon making reference to the detailed description which follows and the accompanying sheet of drawings in which preferred embodiments of a refractory metal retainer and heat shield assembly are shown and described and wherein the principles of the present invention are incorporated by Way of illustrative examples. Of these drawings:

FIGURE 1 is an exploded view of a heat shield assembly together with the retaining and fastening device.

FIGURE 2 is a plan view of a heat shield assembly held together with the nut and bolt.

FIGURE 3 is a cross-sectional view of the retaining device taken along the line 3-3 of FIGURE 2. The nut and bolt are particularly shown together with a helical wound spacer element which is disposed between the plates of the heat shield.

Referring to FIGURE 1 of the drawing, a pair of heat shields 1 and 3 are shown for convenience, although more or less may be used. These shields or baffie plates, which may be fabricated of plates of suitable refractory metals such as tungsten, columbium, molybdenum or tantalum,

3 V are generally 0.005 to 0.050 inch'thick. Preferably, a pair of apertures 5 and? are formed in heat shield 1 and 1 wire upon a tungsten mandrel of 0.0557 diameter at 100% a similar, coaxially positioned pair 2 and 4 are formed. 1

in heat shield 3. Each of the apertures are preferably of a diameter slightly larger then helicallywound bolts 9 and 11 so that the latter may easily pass therethrough. The

, .exact size and shape of the heat shield may bevaried to meet the needs of the particular furnace into which they are to be installed and although flat rectangular plates are shown many other shapes maybe used, as desired.

Because the heat shields 1 and 3 must be separated from each other to obtain maximum reflectance in the furnace,

a pair of refractory metal spacer elements 15 and 17 are slipped over the helically wound bolts 9 and 11 and dis posed between the heat shields 1 and 3. Preferably these spacer elements 15'and 17 are formed of helical windings having a pitch of about-100%. The internal bore diam eters should be larger then the outside diameters of the bolts 9 and 11 so that they may be easily installed. The outside diameter must be sufiicient to abut-against the heat shields 1 and 3 and not pass through any of the apertures 2, 4, and 7. Although we prefer to use refractory metal coils for the spacers, it may be observed that other shapes and other materials may be used. For example,

it may be practical to use a tubular sleeve formed of graphite or refractory metal carbides so long as the material used does not introduce contaminents into the furnace'.. The use of a helically coiled spacer does however, add quite a bit of stability to the unit upon assembly.

Tightening of nuts 19 and 21 against the heat shieldwill thebolt at one end so that a bolt having a head is made of a continuous winding. Furthermore, in some cases the bolt head maybe eliminated and one end of the bolt may be screwed directly into. a tapped and threaded hole disposed in the furnace wall.

In FIGURE 2 the positioning of the spacer elements and 17 between the heat shields 1 and 3 is shown. As

pitch to an appropriate length, for example 2% feet. The long length of coiled tungsten can then be severed into any desired length bolt and leaving the mandrel within the coiling can add additional stability thereto. Any ofithe coiling techniques described are: those conventionallylused in the art and other refractory metals can be used as desired. Although we prefer to use a cylindrical mandrel having regular sides, it is also possible to use a threaded mandrel and unscrew it from the winding rather then acid-leaching.

The range of wire sizes that can beused to. form retainers can-be varied rather widely. For example, it is quite possible to use wire having diameters ranging from 0.005 to 0.125 inch. The size of the mandrel can be varied between about 0.005 to 0.5 inch or even larger.

it is-quite apparent that the devices may be used for many will be seen, bolt heads 23 and 25 are disposed at one 1 end of the. bolt (not shown) and bntted against heat shield 3. Spacer elements 15 and IT are slipped over the bolt and disposed between the heat shields 1 and 3. Then, I

nuts 19 and 21 are threaded 'upon the bolt and tightened to secure a rigid fit. Although we have shown only two heat'shields spaced from each other, it is quite common to use a large series of such heat shields tied together upon common bolts :and spaced from each other by spacers similar to that shown and described.

In FIGURE 3, a cross sectional view of the by conventional techniques. Particularly referring to tungsten heat shield assemblies, nut 21 (and bolt head 23) can be made by coiling a 0.035" diameter tungsten 'wire on'a 0.115"- diameter steel rod at 100% pitch to a length of 2.5 feet. The mandrel is then removed by acid washing and the coiling is cut to approximately W lengths, although other lengths may be used whendesired. The spacers 15 and 17 can be made by coiling 0.035 diameter tungsten 'wire on a'0.128 diameter steel manheat shield assembly of our. invention is shown. Wrapped upon'a' refractory metal mandrel 27 are the helical windings of other applications where a nut and bolt is heated to extremely. high temperatures. Thus, it is apparent that modifications and changes maybe madein the instant invention, but it is our intention however to be limited only by the scope ofthe following claims. 1

We claim as our invention: j

1. A retaining and securing device for high temperature applications comprising incombination: a first longitudinally extendingsubstantially irresilient seriesof helically wound convolutionsof a refractory metal selected from the group consisting of tungsten, tantalum, columbium andrnolybdenum, said convolutions-having a sub- I stantially circular and'uniform.cross section, the external surfaces ofsaid first series of helically. wound convolutions forming a male thread, said first series having a pitch of about-100%; means positioned atone end of said first series of helically wound convolutions forming an abutment for elements disposedthereon; a second longitudinally extending, substantially irresilient series of helically wound convolutions of a refractory metal, said convolutions havingga substantially circular and uniform cross, section, theinternal surfaces-of said second series of helically wound convolutions forming a female thread, said second series having a pitch of about 100%, said thread of said second series of convolutions screwed upon the thread of said first series of convolutions.

. 2. .A retaining and securing device for high-temperature applications comprising in combination: a first longitudinallyextending, substantially irresilient series of helically wound convolutions of arefractory metal selected from the group consisting of tungsten, tantalum, columbium and molybdenum disposed upon a refractory metal mandrel, said convolutions having a substantially circular and uniform cross section, the, externalsurfaces of said first self-supporting, it is quite possible to remove the mandrel series of helically wound convolutions' forming a male thread, said first series having apitchof about 100%; means positioned atone end of said first series of helically woundlconvolutions{forming an abutment for elements disposed thereon; a second longitudinally extending, substantially irresilientseries of helically wound convolutions of a refractory metah'said convolutions having a substantially'circular and uniform cross section, the in- ;ternal surfaces of said second series of helically wound convolutions forming a female thread, said second series having a' pitch of about 100%, said thread of said second drel at 100% pitch. *Similarly as with the nut, the mandrel is removed and the spacers canbe cut to any-desired length, for example one half inch. The .bolt 11 can be series offlconvolutions screwed upon the threadrof said first series of convolutions. '3.'.A"retainin'g' and securing device for high temperature applications comprising in combination: a first longitudinally extending, substantially irresilient series of helically wound convolutions of a refractory metal selected from the group consisting of tungsten, tantalum, columbium and molybdenum, said convolutions having a substantially circular and uniform cross section and a pitch of about 100%, the external surfaces of said first series of helically wound convolutions forming a male thread, said first series having a pitch of about 100%; means positioned at one end of said first series of helically wound convolutions forming an abutment for elements disposed thereon; a second longitudinally extending, substantially irresilient series of helically wound convolutions of a refractory metal, said convolutions having a substantially circular and uniform cross section, the internal surfaces of said second series of helically wound convolu tions forming a female thread, said second series having a pitch of about 100%, said thread of said second series of convolutions screwed upon the thread of said first series of convolutions.

4. A heat shield assembly adapted to be disposed in a high temperature furnace comprising in combination: at least one baffie plate having at least one aperture therein, at least one first series of longitudinally extending, substantially irresilient, helically Wound convolutions of a refractory metal selected from the group consisting of tungsten, tantalum, columbium and molybdenum, having a substantially circular and uniform cross section disposed in said aperture in said baffle plate, the external surfaces of said first series of said helically wound convolutions forming a male thread, said first series having a pitch of about 100%; means forming an abutment for said baffle plate positioned at one end of said first series of helically wound convolutions; a second longitudinally extending, substantially irresilient series of helically wound convolutions of a refractory metal screwed onto the other end of each of said first series of helically wound convoltions, said convolutions of said second series having a substantially circular and uniform cross section, the internal surfaces of said second series of helically wound convolutions forming a female thread, said second series having a pitch of about 100%.

5. A heat shield assembly adapted to be disposed in a high temperature furnace comprising in combination: at least one bafile plate having at least one aperture therein, at least one first series of longitudinally extending, substantially irresilent, helically wound convolutions of a refractory metal selected from the group consisting of tungsten, tantalum, columbium and molybdenum having a substantially circular and uniform cross section disposed in said aperture in said baflle plate, the external surfaces of said first series of helically wound convolutions forming a male thread, said first series having a pitch of about 100%; a mandrel disposed within said first series of helically wound convolutions; means forming an abutment for said baflie plate positioned at one end of said first series of helically wound convolutions; a second series of longitudinally extending, substantially irresilient, helically Wound convolutions of a refractory metal screwed onto the other end of each of said first series of helically wound convolutions, said convolutions of said second series having a substantially circular and uniform cross section, the external surfaces of said second series of helically Wound convolutions forming a female thread, said second series having a pitch of about 100%.

6. A heat shield assembly adapted to be disposed in a high temperature furnace comprising in combination: at least two baffle plates having at least one aperture disposed in each of said baffle plates, each of said apertures being substantially coaxially aligned; at least one longitudinally extending, substantially irresilient first series of helically wound convolutions of a refractory rnetal selected from the group consisting of tungsten, tantalum, columbium and molybdenum having a substantially circular and uniform cross section disposed in said apertures in said bafiie plates, the external surfaces of said first series of helically wound convolutions forming male threads, said first series having a pitch of about 100%; means forming a spacer slidably positioned over said first series of helically wound convolutions between said baffle plates and adapted to space said baffle plates from each other; means forming an abutment for said baffie plates positioned at one end of said first series of helically wound convolutions; a second series of longitudinally extending, substantially irresilient helically wound convolutions of a refractory metal screwed onto said first series of helically Wound convolutions, said convolutions of said second series having a substantially circular and uniform cross section, the internal surfaces of said second series of helically wound convolutions forming a female thread, said second series having a pitch of about 100%.

References Cited by the Examiner UNITED STATES PATENTS 776,737 12/04 Greenfield -32 809,880 1/06 Woolldridge et a1. 85-32 1,861,532 6/32 Hough 851 3,061,054 10/62 Simmonds 189-34 RICHARD W. COOKE, 111., Primary Examiner. 

1. A RETAINING AND SECURING DEVICE FOR HIGH TEMPERATURE APPLICATIONS COMPRISING IN COMBINATION; A FIRST LONITUDINALLY EXTENDING SUBSTANTIALLY IRRESILIENT SERIES OF HELICALLY WOUND CONVOLUTIONS OF A REFRACTORY METAL SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN, TANTALUM, COLUMBIUM AND MOLYBDENUM, SAID CONVOLUTIONS HAVING A SUBSTANTIALLY CIRCULAR AND UNIFORM CROSS-SECTION, THE EXTERNAL SURFACES OF SAID FIRST SERIES OF HELICALLY WOUND CONVOLUTIONS FORMING A MALE THREAD, SAID FIRST SERIES HAVING A PITCH OF ABOUT 100%; MEANS POSITIONED AT ONE END OF SAID FIRST SERIES OF HELICALLY WOUND CONVOLUTIONS FORMING AT ABUTMENT FOR ELEMENTS DISPOSED THEREON; A SECOND LONGITUDINALLY EXTENDING, SUBSTANTIALLY IRRESILIENT SERIES OF HELICALLY WOUND CONVOLUTIONS OF A REFRACTORY METAL, SAID CONVOLUTIONS HAVING A SUBSTANTIALLY CIRCULAR AND UNIFORM CROSS SECTION, THE INTERNAL SURFACES OF SAID SECOND SERIES OF HELICALLY WOUND CONVOLUTIONS FORMING A FEMALE THREAD, SAID SECOND SERIES HAVING A PITCH OF ABOUT 100%, SAID THREAD OF SAID SECOND SERIES OF CONVOLUTIONS SCREWED UPON THE THREAD OF SAID FIRST SERIES OF CONVOLUTIONS. 